1. Field of the Invention
This invention relates to a vibration dampening assembly. In one of its aspects, the invention relates to a vibration dampening assembly for use in a suspension system in a vehicle and, in particular, in a suspension system between a cab and a frame of a truck. In another of its aspects, the invention relates to a suspension system for use, for example, between a cab and a frame of a truck.
2. State of the Prior Art
In Conaway et al. U.S. Pat. No. 5,253,853, a vibration dampening device is disclosed for use between a truck body and a cab. The vibration dampening device includes a link pivotably mounted at one end to the frame of a truck and pivotably mounted at another end to a lever. The lever is pivotably mounted at one end to a suspended member, for example, a cab of a truck and is pivotably mounted at another end to one end of a shock absorber. The other end of the shock absorber is pivotably mounted also to the suspended body or cab at a pivot point spaced from the pivot point mounting of the lever first end to the suspended body. This device is said to isolate a suspended body or truck cab from the force vibration of the supporting body and provide a non-linear response to vibrational movement of the suspended body with respect to the support body. Whereas some beneficial vibration isolation takes place with a device according to the Conaway et al. '853 patent, there are some operational limitations in the design of a suitable dampening assembly and there are practical difficulties in manufacturing this vibration dampening device with proper design characteristics. The distance between the axes of pivot mounts of the lever to the suspended body (main pivot) and the lever to the link controls the relative amount of vertical movement between the suspended and supporting bodies and influences the displacement versus resistive force characteristics of the device. It has been found that the axes of these two pivots should be spaced about 3/8" apart. Greater spacing between these two pivot axes gives a wider range of uncontrolled oscillation, and results in a fairly abrupt transition between the oscillation force and dampening force. A smooth transition between the oscillation and the dampening portion of the force versus displacement curve is necessary for an acceptable dampening device. However, at 3/18" spacing between the pivot axes, manufacture of the dampening device becomes difficult because the bearings of the pivot axes overlap. However, the geometry of the device precludes this type of arrangement.